Various polymers having liquid crystal characteristics have already been developed. Such polymers generally have the mesogen group represented by formula: ##STR2## wherein X represents a direct bond, --(C.dbd.O)--O--, --(C.dbd.O)--NH-- or --N.dbd.N--, R represents hydrogen, cyano group or methoxy group;
present in the polymer backbone (main chain type liquid crystal polymer) or in the side chain (side chain type liquid crystal polymer).
Although the mesogen group shown above is introduced into the polymer via various bonds (e.g. ester bond), few polymers having urethane bond have been reported.
In the main chain type liquid crystal polymer having a higher molecular weight, hydrogen bond characteristics of the urethane bond are considered to serve to bend the terminal of the molecule, whereby reducing the interaction of the mesogen group. Similar tendency is suspected also in the cases of side chain type liquid crystal polymers. Therefore, there are few studies on liquid crystal polymers having urethane bonds in their side chains.